Method of manufacturing a solar collector panel

ABSTRACT

A method of manufacturing an integral one-piece solar collector panel by a rotational moulding process is disclosed. The solar collector panel has a plurality of fluid ways extending between opposed ends and transverse headers opening into the open ends of the fluid ways. The panel is moulded by a rotational moulding process using mould faces with a non planar topography, eg in the form of a plurality of lines projecting outwardly proud of the remainder of the mould plate. This enables areas of the moulded body to be formed that are not hollow and form a solid wall in the moulded panel and other areas of the body to be formed that are hollow and form the fluid ways and headers. After the moulding of the panel has taken place the two opposed mould faces are moved towards each other to cause the contacting layers of mould material to firmly adhere to each other. This post moulding treatment step is not used in standard rotational moulding processes. The manufacturing process of the invention enables collector panels to be produced at substantially less cost than known prior art methods of making collector panels.

[0001] This invention relates to a method of manufacturing a solar collector panel and to a panel produced by the process. It also relates to a solar hot water heater incorporating the aforesaid panel.

[0002] This invention relates particularly but not exclusively to a solar collector panel for a domestic hot water system for supplying heated water for domestic use that is mounted on the roof of a dwelling. It will therefore be convenient to hereinafter describe the invention with reference to this example application. However it is to be clearly understood that the invention is capable of broader application. For example, the invention may also be used to preheat water for low level heating applications, eg to heat swimming pool heaters, aquaculture ponds, manufacturing processes and the like.

BACKGROUND TO THE INVENTION

[0003] Water heaters that use solar energy are well known. Typically such heaters comprise a solar collector panel for heating up water and a water tank for storing the heated water prior to use. The panel and typically also the tank are mounted on a roof with a sloping orientation having an upper end and a lower end and positioned so as to catch radiant energy from the sun. Structurally the panel has a plurality of fluid ways extending between the upper and lower ends and the panel also has upper and lower headers communicating with the open ends of the fluid ways. The heater also has at least two conduits, eg located externally of the collector panel, coupling the panel to the tank. Specifically one said conduit couples the upper header with the tank and the other said conduit couples the tank with the lower header. Thus the heater overall facilitates water flow up through the fluid ways and into the tank.

[0004] In use solar energy from the sun heats up the panel by radiant heat transfer which in turn transfers heat to water in the fluid ways by convective and conductive heat transfer. This causes the water to expand and decrease in density causing it to travel up the fluid ways and into the upper header. From there the water passes into the tank for storage from where it is drawn for use when required. Within the tank the warmer water tends to move towards the top of the tank because of natural fluid convection within the tank. Inside the tank the cooler water is displaced by the warmer water to the bottom of the tank. A conduit links the bottom of the tank with the lower header and water is drawn off the tank as freshly heated water from the upper header is introduced into the tank. This water then passes from the lower header into the fluid ways where it is presented for heating in the manner described above and the cycle is repeated. This principle of circulating water through this heating system by natural convection is known as a thermosiphon effect and is well known. Using this system it is possible to heat water up to a temperature of 70° C. or even higher for use as domestic hot water for cleaning and washing.

[0005] This basic structure and principle of operation of the thermo-siphon effect has been described in many publications. Some such publications are AU 65934/94, AU 24885/95 and AU 15031/97. The contents of these specifications are hereby explicitly incorporated into the specification by direct cross reference.

[0006] However the heaters described above have some structural shortcomings. Firstly many solar collector panels comprise an assembly of pipes and sheets that is fabricated in a fairly elaborate metal working process. The fluid ways are made of pipes as are the headers and these have to be attached to each other, eg by welding or soldering. The pipes in turn are housed within a housing including a perimeter frame that has to be fabricated and the housing then has to be attached to the pipes. In addition couplings have to be provided for attachment of the external pipes to the headers in the panel. Finally a cover sheet is mounted over the top of the pipes to reduce convection heat loss from the pipes. As a result manufacture of the panel is fairly expensive.

[0007] In addition existing heaters also have some operational shortcomings. The pipes and headers are welded or soldered and these welds or solders are prone to failure when the piping is exposed to cold temperatures, eg frost conditions. The expansion of water in the pipes when it freezes causes these failures. The cost of repairing these welds or solders is substantial as the repairs need to be carried out by a qualified fitter usually on site.

[0008] A further operational shortcoming is that the metal pipes are susceptible to scale build up due to salts in the water such as calcium carbonate. This problem is well known in the boiler and water heater arts. While technology is available to resist this problem and/or clean the pipes the cost of de-scaling these pipes is substantial. These above two operational shortcomings provide an incentive to move away from metal or steel pipes.

[0009] There is almost universal acceptance of the desirability of using solar heating to heat domestic water. It is a renewable energy source and reduces the reliance on electrical energy that is produced by coal fired power stations. This is recognised by regulators and governments around the world. For example in Australia financial incentives in the form of rebates are offered to people installing solar hot water heating systems in their homes.

[0010] Applicant believes that the advantages of converting to solar heating are clear and that a major impediment to the widespread uptake of the technology is the capital cost of installing the systems and the maintenance problems described above. In particular the cost of the collector panels which are fabricated from metals is very high. Applicant believes that if these problems could be significantly reduced there would be a quantum increase in the uptake of the technology. Applicant believes that this would have the potential to make the use of solar heaters in domestic homes a standard feature in areas having high levels of sunlight.

[0011] Clearly therefore it would be advantageous if a lower cost solar heating system could be devised. Specifically it would be advantageous if a new and different way of manufacturing the panels could be devised that simplified the structure of the panels and reduced the cost of the panels.

SUMMARY OF THE INVENTION

[0012] According to one aspect of this invention there is provided a method of manufacturing a solar collector panel having two opposed ends defining a plurality of fluid ways having open ends extending there between and defining transverse headers at said opposed ends opening into the open ends of the fluid conduits, the method comprising:

[0013] providing a mould defining opposed mould faces having a non uniform spacing between the mould faces across the surface of the faces;

[0014] inserting a mould material into the mould and moulding a body by a rotational moulding process so as to produce a layer of material of substantially uniform thickness across the surface of the mould faces, whereby the non-uniform spacing between the mould surfaces causes the body to be moulded with areas that are not hollow and other areas that have hollow passages defined therein, the hollow passages defining the fluid ways and transverse headers and the non hollow areas defining walls between the fluid ways; and

[0015] allowing the mould and body to cool after the layer of material has been moulded onto the mould surface and then removing the body from the mould whereby to provide a moulded solar collector panel for use.

[0016] The technique of rotational moulding is a well known moulding technique that can be used to manufacture articles of intricate shape. It involves rotating a mould about two orthogonal axes to deposit an even layer of mould material onto the surface of the mould. The shape of the article is determined by the shape of the mould. The thickness of the layer of deposited material can be controlled by metering the quantity of mould material that is introduced to the mould at the start of the process.

[0017] Firstly the invention involves an appreciation that by a suitable variation of the contour or topography of the mould surfaces of the mould, rotational moulding can be used to produce a body having a plurality of fluid ways. Specifically the applicant appreciated that rotational moulding could be used to produce a body having a plurality of parallel extending fluid ways in one direction and interconnecting headers at each end of the fluid ways extending in a transverse direction. This works on the principle that rotational moulding deposits an even layer of material on the mould surface and that by appropriate configuration of the mould surfaces and spacing of the mould surfaces a body having specific internal passages can be moulded.

[0018] The fluid ways and headers are formed by having the relevant areas of the opposed mould surfaces spaced further apart from each other than the other areas which are relatively closer together. The layers of mould material on the mould faces in these other areas adhere to each other and form the walls intermediate the fluid ways. Specifically this is achieved by spacing the opposed surfaces of the mould parts away from each other by a distance less than or equal to twice the thickness of material such that the layers of material are in contact with each other forming said walls between adjacent fluid ways.

[0019] The invention also involves the appreciation that a solar collector panel might be able to be manufactured, eg as a single piece of plastics material, in a moulding process and that this would be a simpler and considerably less expensive way of producing a panel than the current metal fabrication techniques. The applicant has also appreciated that if a solar collector panel was made of plastics material it would not be susceptible to scale deposits and the solder and welding failures that frequently occur in metal collector panels and which require costly maintenance.

[0020] The applicant has also appreciated that plastics material has a sufficiently high coefficient of thermal conductivity to be used in a heat transfer application where it is required to conduct heat and that it has sufficiently resilient engineering properties to be used in an application where it is deliberately exposed to the suns rays for a number of years without undergoing substantial deterioration.

[0021] The non-uniform spacing between the mould faces may comprise at least one said mould face having a non planar topography across its surface whereby to form the non hollow walls and hollow fluid ways.

[0022] The non planar topography may comprise at least one mould face having one or more areas projecting outwardly proud of the remainder of the mould face.

[0023] The method may further include the further step of moving the mould faces and thereby the layers of moulded material on the faces towards each other a certain distance after the moulding step has been carried out and before the body is given time to cool, to urge the layers of moulded material forming said non hollow areas of the body firmly into adhesive contact with each other to achieve fluid sealing of the walls between adjacent fluid ways. The mould faces may be moved towards each other by a distance of at least 5 mm, preferably 10 mm-50 mm, more preferably 15 to 30 mm.

[0024] This squashes the layers associated with each mould surface firmly into adhesive contact with each other and seals the layers to each other so that fluid cannot flow laterally out of one fluid way and into the adjacent fluid way. This is important to efficaciously seal two fluid ways from each other so they function much like the pipes of conventional fabricated solar panels. This is known in the moulding art as achieving satisfactory kiss off.

[0025] Further the step of moving the mould faces towards each other also confers an ability to control the diameter of the fluid ways by appropriate adjustment of the distance that the mould parts are moved towards each other.

[0026] Typically the mould comprises two mould plates each of which defines a said mould face and which in use defines a closed mould cavity. Conveniently both of said mould faces may have one or more said areas projecting outwardly relative to the remainder of the mould face and said outwardly projecting areas on the faces may be vertically aligned with each other. The one or more outwardly projecting areas may comprise a plurality of substantially linearly extending lines extending between opposed ends of the mould faces, eg parallel to each other but terminating short of said ends of the mould faces.

[0027] Each of the mould faces may have further areas that are recessed relative to the remainder of the mould face whereby to form headers, eg of greater diameter than the fluid ways, at each end of the panel.

[0028] The mould faces may be substantially rectangular and may define a substantially rectangular mould surface.

[0029] The mould may also include mould formations for moulding inlet and outlet ports in the body in the rotational moulding operation. Further optionally the inlet and outlet ports may be moulded with a screw thread formation thereon for attaching a conduit to the panel.

[0030] Typically the inlet port will be located on one side of one end of the panel and the outlet port will be located on the other side of the other end of the panel.

[0031] Conveniently the panel may be made from polyethylene, eg HDPE, or polypropylene or indeed any other engineering plastics material.

[0032] The invention also extends to a panel produced by the method described above and that can be used as a solar collector panel in a solar heating system.

[0033] According to another aspect of the invention there is provided a panel comprising a body of material having two ends and defining a plurality of parallel fluid ways extending between the opposed ends, and also defining headers at each end of the body extending transverse to the fluid ways and communicating with the fluid ways, the panel being manufactured from a mould material in a mould defining opposed mould faces using a rotational moulding process, wherein at least one mould face has a non planar topography across its surface whereby to form a moulded body having areas that are not hollow and form the walls between the passageways and other areas that have hollow passageways and form the fluid ways and the headers.

[0034] The panel may be made of a plastics material, eg an engineering plastics material, and may be formed as an integral one piece body. The panel may have a substantially rectangular configuration with two major surfaces and the fluid ways may extend parallel to two sides of the rectangle and the headers may extend substantially parallel to the other two sides of the rectangle. The panel may further include at least one fluid inlet port defined therein towards one end of the body and at least one outlet port defined therein towards the other end of the body. The inlet and out let ports may be formed in the body during the process of moulding the body.

[0035] The two major surfaces of the panel may be moved inwardly towards each other, eg squashed, during manufacture of the panel to cause the layers of mould material on the opposed mould faces that are in contact with each other to firmly adhere to each other. The two major surfaces are squashed after the mould material has been moulded onto the faces of the mould but it is cooled.

[0036] According to yet another aspect of this invention there is provided a solar heater comprising at least one panel as described above according to the previous aspect of the invention mounted on a support.

[0037] The support may be a collector box defining a perimeter frame within which the collector panel/s are snugly received. Further the collector box may include a UV and light transparent sheet mounted over the panel/s.

[0038] The heater may include a plurality of collector panels, eg coupled in parallel.

[0039] The heater may further include a tank operatively coupled to the panel/s whereby water heated up in the panel/s can be transferred to the tank for storage prior to use.

[0040] The heater may also include a first conduit coupling one end of the panel/s to the tank and a second conduit coupling an opposed end of the panel/s to the tank.

[0041] The heater may also include a safety relief valve for venting any pressure that does build up inside the conduit, tank or panel/s.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0042] A method of manufacturing a solar collector panel and a solar collector panel in accordance with the invention may manifest it self in a variety of forms. It will be convenient to hereinafter describe in detail one preferred embodiment of the invention with reference to the accompanying drawings. The purpose of this detailed description is to instruct persons interested in the subject matter of the invention how to carry the invention into practical effect. It is to be clearly understood however that the specific nature of this detailed description does not supersede the generality of the preceding broad description. In the drawings:

[0043]FIG. 1 is a schematic three dimensional view of a solar water heater using a thermo-siphon principle of circulating water around the heater;

[0044]FIG. 2 is a schematic three dimensional view of a fabricated solar collector panel for the solar heater of FIG. 1;

[0045]FIG. 3 is a perspective view of a solar collector panel manufactured in accordance with the invention;

[0046]FIG. 4 is a perspective view of a preferred embodiment of a solar connector panel according to the invention;

[0047]FIG. 5 is a view from above from the solar panel from FIG. 3;

[0048]FIG. 6 shows a left side view of the embodiment of FIG. 4;

[0049]FIG. 7 is a cross-sectional view through the panel of FIG. 3, showing the fluid ways;

[0050]FIG. 8 is a sectional view through the panel of FIG. 3 in a longitudinal direction showing the transverse headers;

[0051]FIG. 9 is a schematic cross sectional view through a rotational moulding apparatus having two opposed mould surfaces for making the panel of FIG. 3 prior to the commencement of the rotational moulding process;

[0052]FIG. 10 is a view of the apparatus of FIG. 9 after the rotational moulding step has been carried out;

[0053]FIG. 11 is view of the apparatus of FIG. 10 undergoing a post moulding processing step in which the two mould surfaces are displaced towards each other urging the layer of mould material on one surface into contact with the adhesive material on the other mould surface;

[0054]FIG. 12 is an exploded three dimensional view of a solar heater in accordance with one embodiment of the invention and having a single solar collector panel;

[0055]FIG. 13 is a three dimensional view of the heater of FIG. 12 in an assembled conduit;

[0056]FIG. 14 is a three dimensional view of a solar heater in accordance with another embodiment of the invention having a plurality of panels operatively connected to each other side by side and showing the modular nature of the panels.

[0057]FIGS. 1 and 2 illustrate well known constructions in the solar heating art and have been described above in the background to the invention. The following description will focus on the collector panel and solar heater of the invention which are illustrated in FIGS. 3 to 14.

[0058] In FIG. 3 reference numeral 10 refers generally to a solar collector panel in accordance with the invention.

[0059] Broadly the panel 10 comprises a body 12 having one end 13 and an opposed end 14. A plurality of parallel extending fluid ways or passages or conduits 15 are defined in the body extending from the end 13 to the end 14. In the illustrated embodiment there are 15 to 20 said fluid ways 15 spaced apart from each other across the width of the panel 10. Each fluid way 15 corresponds to a strip or band on the external surface of the body 12 intermediate linearly extending channels or recesses 16. The correspondence between the fluid ways 15 and the ridges will become clearer after the moulding process has been described below. Overall the illustrated panel 10 has a flat rectangular configuration with two major surfaces namely an upper and a lower surface and with the fluid ways extending longitudinally between opposed ends of the panel.

[0060] The panel 10 also includes transverse headers 18 and 19 that are defined in each end of the body 12 extending transverse to the direction of the fluid ways 15. Each end of each fluid way 15 opens into a said header 18 or 19 such that the headers 18, 19 and fluid ways 15 are in fluid communication.

[0061] The panel 10 also includes an inlet port 20(a) that opens into the header 19 and an outlet port 20(b) that opens into the other header 18. Further the inlet and outlet ports 20(a) and 20(b) are located on opposed sides of the panel 10. Similar ports 22(a) and 22(b) are arranged opposite to ports 20(a) and 20(b).

[0062]FIG. 4 shows a preferred embodiment of this solar panel wherein, as opposed to the embodiment shown in FIG. 3, the inlets and outlets are arranged, transverse to the fluid ways, whereby the panel 10 includes an inlet port 21(a) or 21(b) that opens into the header 19 and an outlet port 17(a) or 17(b) that opens into header 18. Preferably, whichever inlet/outlet ports are to be used, they are to be arranged in opposite sides of the panel.

[0063] Using the embodiment in FIG. 3 cold water would enter the panel from the bottom of the storage tank through inlet 20(a) into header 19. Ports 22(a) and 22(b) would be blanked off, hot water would thermosiphon into header 18 and through outlet 20(b) into the storage tank at a higher level than the cold water out.

[0064] Using the embodiment in FIG. 4 cold water would enter from the bottom of the storage tank through inlet 21 (a) via a conduit from storage tank to header 19, ports 21(b) and 17(a) would be blanked off, hot water would thermosiphon into header 18 and through outlet 17(b) into the storage tank at a higher level than the cold water out.

[0065] An advantage of this embodiment shown in FIG. 4 is that since the panel is symmetrically arranged and the inlet/outlet ports run transverse the fluid ways, the panel is less susceptible to the effects of possible buckling.

[0066]FIG. 7 shows in some detail the fluid ways 15 that are defined in the body by the rotational moulding process. This drawing shows how the areas of the mould face illustrated in FIG. 9 that are raised relative to the remainder of the face form the non-hollow areas of the body forming the walls 23 between the adjacent fluid ways 15. The outwardly projecting areas on the mould faces that are ridges form recesses in the moulded body which forms a solid wall in the body.

[0067]FIG. 8 shows the headers 18, 19 formed at the end of the fluid ways 15 transverse to the fluid ways 15. Like the fluid ways 15 the headers are formed by adjusting the spacing between the opposing mould faces. The lines or ridges that are raised relative to the remainder of the mould face terminate short of the ends of the panel to provide the transverse headers 18, 19 at the ends of the fluid ways 15.

[0068]FIG. 9 illustrates a rotational moulding apparatus 30 for moulding the panel 10. Broadly the apparatus 30 comprises an upper mould plate 31 and a lower mould plate 32 that come together in an opposed relationship to define the closed mould. Each of the mould plates defines a mould face 33 or 34 of non planar topography that forms the shape of the body, ie panel, that is moulded from the apparatus. Each mould surface has areas in the form of lines or ridges that project outwardly relative to the remainder of the mould face to form non hollow portions of the moulded body between the fluid ways. The other areas of the surfaces form the hollow portions of the moulded body that serve as the fluid ways and headers.

[0069] The apparatus 30 also includes the other components of a typical rotational moulding apparatus. As these features would be well known to a person skilled in the art and do not form part of the invention they are not shown in the drawings and will not be described in the specification.

[0070] The apparatus does have one feature that is a modification of a standard rotational moulding apparatus. The mould plates 31, 32 are mounted so that they may be displaced inwardly towards each other and then also be displaced back outwardly relative to each other. This feature is used in a post moulding treatment step that is specific to this invention that enhances the adhesion of the contacting layers of material to each other and thereby the sealing off of adjacent fluid ways 15. The plates may be moved a distance of 5 mm to 100 mm towards each other, more typically 10 mm to 50 mm towards each other. The distance will vary for different applications and materials.

[0071] The above displacement of the plates towards and way from each other may be accomplished by having the mould plates mounted on a slide and locking mechanism. The slide guides the plates towards and away from each other while maintaining the plates in alignment with each other. The locking mechanism permits the plates to be checked at a desired spacing from each other and held in this position for the post moulding treatment step. While the arrangement described above has been found to be particular useful it is to be clearly understood that a number of other ways of achieving the same result would immediately suggest itself to a person skilled in the art and the apparatus is not to be limited to a slide and locking mechanism.

[0072] In use a metered amount of mould material is introduced to the interior of the mould and the mould parts are closed. The amount of material that is introduced to the mould is calculated very carefully. This is because the amount of material put in initially determines the thickness of the layer of mould material formed on the mould faces. In this particular application it is particularly important that the layer of material is the correct thickness because this is necessary to form a body having hollow fluid ways and solid walls in between the fluid ways. The mould is then heated up using a radiant heater although clearly convection and conduction heaters can also be used. All that is required is that the mould plates be heated up to a temperature that softens and melts the mould material. The interior of the mould is not pressurised during the moulding operation. The mould is then rotated about two orthogonal axes in the usual way for a rotational moulding apparatus. The rotation spreads the mould material evenly across the mould surface as it softens and melts. A characteristic of rotational moulding is that it provides an even layer of material across the mould surface and by appropriate design of the shape of the mould a body defining a number of passages or fluid ways with walls between the fluid ways can be moulded. The external shape of the moulded article is determined by the shape of the mould surfaces and not by the rotational motion of the mould. Further by metering the amount of material that is introduced to the mould the thickness of the layer of material deposited on the mould surfaces can be controlled. This produces a moulded body as shown in FIG. 10.

[0073] The body formed by the process above could be used directly as a solar collector panel 10. However the Applicant has discovered a post moulding step that substantially enhance the strength and integrity of the finished panel. This step involves moving the opposed mould faces towards each other to enhanced the adhesion of the mould material

[0074] As shown in FIG. 11 once the moulding has been completed and before the body is allowed to cool significantly the mould parts are moved towards each other to squash the contacting layers of mould material firmly into adhesion with each other. This causes the layers to adhere efficaciously to each other so that they are disinclined to part or separate when water is passed through the passageways. This achieves a superior kiss off of the moulded material on opposed surfaces of the mould. The extent of the displacement of the plates towards each other in this step can also be used to vary the height or diameter of the fluid ways and headers formed in the body.

[0075] After this step the mould plates are allowed to cool back to room or ambient temperature and then the body is removed from the mould. The moulded body is an integral one piece body of plastics material complete with formed fluid ways and headers and inlet and outlet ports that is suitable for use as a solar collector panel. It is formed in a single process which combines conventional rotational moulding with the further step of moving the mould plates towards each other.

[0076] Applicant has tested a panel made by the process described above and found that it worked well in a solar heating system using a thermosiphon principle. At the same time the fluid ways had a consistent clearance along their length and opened out into the headers through openings of predictable and reproducible size. Further the headers had a clearance of even dimension along their length. In summary the flow passages produced in the body by the moulding process are suitable for the hydraulic flow of water there through at the flow rates and pressures that are encountered in a solar water heater. The panels remained laterally sealed from each other and showed no tendency for the layers forming the walls between the fluid ways to lift and separate when water at moderate pressure was pumped through the fluid ways. This was the case even after the panel had been used for a considerable time. This demonstrates that the contacting layers of material forming the walls between the fluid ways had adhered efficaciously to each other.

[0077] The heat transfer properties of the collector panel were comparable to those obtained with prior art fabricated panels and the performance of the heater using the panel described above was broadly comparable to that obtained from a prior art panel. Further based on the engineering specifications of the plastics that are used and information obtained from the use of the plastics in other applications where they are exposed to the sun Applicant is confident that the panel will not undergo significant deterioration due to light and UV radiation. The resistance to UV induced deterioration is conferred by modifiers in the plastic.

[0078]FIGS. 12 and 13 show a solar heater assembly including a panel in accordance with the invention. The solar heater assembly is indicated generally by reference numeral 50. Where appropriate the same reference numerals will be used to refer to the same components as in the previous drawings.

[0079] The panel 10 is received within a collector box 51 having a base 52 and a perimeter frame 53. The panel 10 fits snugly within the perimeter frame 53 of the box 51. Conveniently a sheet of insulation 54 may be sandwiched between the base 52 of the collector box 51 and the panel 10 to resist heat loss from the hot water flowing through the panel 10 to the surrounding environment including the box 51 and a roof on which the box 51 is mounted. A sheet of glass 55 is mounted over the panel 10 to form the top layer of the box. The glass permits UV and visible light radiation to pass there through but resists heat loss from the panel by convection.

[0080] The panel 10 is coupled to a tank 57 which is located proximate thereto. The tank is coupled to the panel by means of external inlet and outlet conduits (not shown).

[0081] In use the system operates by the same thermosiphon principle described above in the background to the invention. The moulded collector panel is functionally equivalent to the fabricated collector panels of the prior art. While the fluid ways and headers are defined by passages within an integral one piece moulded body of plastic rather than separate pipes the two are functionally equivalent. The heater can be used to heat water up to a temperature suitable for use as hot water in a domestic environment.

[0082]FIG. 14 illustrates a heater in accordance with the invention that is a variation on the heater shown in FIG. 13.

[0083] This heater 50 comprises a number of panels 10, eg three, received within the collector box 51 and positioned side by side. The panels 10 are essentially connected in parallel with each other. That is water that is returned to the panels makes a single pass through one of the panels and is then displaced back into the tank.

[0084] The addition of further collector panels 10 in parallel confers additional heating capacity on the heater. The heater is modular in the sense that a single size collector panel can be manufactured in a moulding operation and then an appropriate number of panels selected to provide a heater with the required heating capacity. It is not necessary to manufacture a number of different sized collector panels.

[0085] In a further embodiment the heater is used to heat swimming pool water that is passed there through and then returned to the pool. The heater typically comprises one or more collector panels mounted on a roof. The inlet port of the collector panels are coupled to the discharge line of a pool pump and this pumps water through the fluid ways of the collector panels where it is heated in the same way as described above. The discharge port of the panels returns the heated water to the swimming pool. Water is thus pumped through the panel in a single pass and that single pass might heat it by several degrees and then it is returned to the swimming pool. In this application water is not continuously circulated through the system using the thermosiphon effect to achieve temperatures of 60 degrees Celsius or higher. It is simply a case of pumping water through the collector panels to effect low level heating.

[0086] An advantage of the solar collector panel described above is that it is formed as a single integral one piece body in a single rotational moulding process. The rotational moulding process enables a body having parallel fluid ways and headers at the ends of the fluid ways to be formed in a single moulding operation. As a result the manufacture of the panel can be accomplished considerably cheaper than with prior art panels that are fabricated from metal.

[0087] The panel is formed from a plastics material that has a suitability high coefficient of thermal conduction and is resistant to degradation by visible light and UV rays. Applicant has found that such a plastic body can be sufficiently efficacious in conducting energy from the sun through to water passing through the fluid ways defined in the moulded body.

[0088] A further advantage of the heater described above is that the panels are modular in the sense that additional heating capacity can be obtained by adding further panels. Additional collector panels can simply be coupled to the system in parallel to provide additional fluid ways and additional heating capacity. Thus only a single size panel need be manufactured.

[0089] It will of course be realised that the above has been given only by way of illustrative example of the invention and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as herein set forth. 

1. A method of manufacturing a solar collector panel having two opposed ends defining a plurality of fluid ways extending there between and transverse headers at said opposed ends opening into open ends of the fluid conduits, the method comprising: providing a mould defining opposed mould faces that are spaced apart from each other wherein the spacing between the mould faces is not equal across the surface of the faces; inserting a mould material into the mould and moulding a body by a rotational moulding process so as to produce a layer of material of substantially uniform thickness across the surface of the mould faces, whereby the unequal spacing between the mould surfaces causes the body to be moulded with areas that are not hollow and other areas that have hollow passages defined therein, the hollow passages defining the fluid ways and transverse headers and the non hollow areas defining the walls between the fluid ways; and allowing the mould and body to cool after the layer of material has been evenly moulded onto the mould surface and then removing the body from the mould whereby to provide a moulded solar collector panel.
 2. A method according to claim 1, wherein the unequal spacing of the mould faces across the surface of the faces is achieved by having an uneven topography on at least one of the mould faces whereby to form the parts of the moulded body that are not hollow and form other areas of the body with hollow passages.
 3. A method according to claim 2, wherein part of said mould face projects outwardly relative to the remainder of said face over said one area to form said non hollow parts of the body and the remainder of the body forms the hollow parts.
 4. A method according to claim 1, including the further step of moving the mould faces and thereby the layers of moulded material on the faces towards each other a certain distance after the moulding step has been carried out and before the body is given time to cool to urge the moulded material on said non hollow areas of the body firmly into adhesive contact with each other to achieve fluid sealing of the walls between adjacent fluid ways and headers.
 5. A method according to claim 4, wherein the mould faces are moved towards each other by a distance of 5 mm to 30 mm.
 6. A method according to claim 3, wherein the mould comprises two mould plates each of which defines a said mould face and which in use defines a closed mould cavity.
 7. A method according to claim 5, wherein both of said mould faces have parts projecting outwardly relative to the mould face and said outwardly projecting parts on the two faces are vertically aligned with each other.
 8. A method according to claim 6, wherein said one or more outwardly projecting parts comprise a plurality of substantially linearly extending lines extending between opposed ends of the mould faces.
 9. A method according to claim 7, wherein linearly extending lines are parallel to each other and each of said lines terminates short of said ends of the mould plates.
 10. A method according to claim 1, wherein the panel is an integral one-piece body having a substantially rectangular configuration having two major surfaces and the panel is made from an engineering plastics material.
 11. A method according to claim 1, wherein the mould faces further include a mould formation for moulding an inlet port in the collector panel towards one end thereof and a further mould formation for moulding an outlet port in he collector panel towards an opposed end thereof.
 12. A panel produced by the method defined above in claim
 1. 13. A panel comprising a body of material having two ends and defining a plurality of parallel fluid ways extending between the opposed ends, and also defining headers at each end of the body extending transverse to the fluid ways and communicating with the fluid ways, the panel being manufactured from a mould material in a mould defining opposed mould faces using a rotational moulding process, wherein at least one mould face has a non planar topography across its surface whereby to form a moulded body having areas that are not hollow and form the walls between the passageways and other areas that have hollow passageways and form the fluid ways and the headers.
 14. A panel according to claim 13, wherein the two mould faces are moved inwardly towards each other during manufacture of the panel to cause layers of mould material on the opposed mould faces that are in contact with each other to firmly adhere to each other.
 15. A solar heater comprising at least one panel as defined in claim 13 and a support on which the panel is mounted.
 16. A solar heater according to claim 15, wherein the support comprises a collector box defining a perimeter frame and the collector panel/s that are mounted on the support are snugly received within the perimeter frame.
 17. A solar heater according to claim 16, further including a UV and light transparent sheet mounted over the panel/s.
 18. A solar heater according to claim 15 wherein the heater includes a plurality of said collector panels mounted on the support and coupled to each other in parallel.
 19. A solar heater according to claim 15, further including a tank operatively coupled to the panel/s whereby water heated up in the panel/s can be transferred to the tank for storage prior to use.
 20. A solar heater according to claim 15, wherein the heater also includes a first conduit coupling one end of the panel/s to the tank and a second conduit coupling an opposed end of the panel/s to the tank. 